Fastener driving tool with improved pneumatic piston retaining means

ABSTRACT

A fastener driving tool includes a cylinder slidably receiving a piston for operating a driver to drive fasteners successively supplied beneath the driver. A main valve selectively supplies compressed air to and exhausts air from above the top of the cylinder to control movement of the piston between normal and displaced positions. The piston is returned by air supplied from a return air space communicating with the bottom of the cylinder when the top of the cylinder is exhausted. Since this return air leaks to the atmosphere as or after the piston is returned, the uppermost part only of the cylinder is provided with different diameter portions cooperating with two spaced sealing means on the piston which trap or are supplied with compressed air to provide an upwardly directed pneumatic bias for releasably holding the piston in its normal position, this bias being removed as soon as the piston moves downwardly into the uniform diameter portion of the cylinder. The piston biasing air is derived directly from the reservoir air or from a valve carried on the piston.

United States Patent Ramspeck Feb. 1, 1972 FASTENER DRIVING TOOL WITHPrimary ExaminerPaul E. Maslousky Attorney-Mason, Kolemainen, Rathburn &Wyss [5 7] ABSTRACT A fastener driving tool includes a cylinder slidablyreceiving a piston for operating a driver to drive fastenerssuccessively supplied beneath the driver. A main valve selectivelysupplies compressed air to and exhausts air from above the top of thecylinder to control movement of the piston between normal and displacedpositions. The piston is returned by air supplied from a return airspace communicating with the bottom of the cylinder when the top of thecylinder is exhausted. Since this return air leaks to the atmosphere asor after the piston is returned, the uppermost part only of the cylinderis provided with different diameter portions cooperating with two spacedsealing means on the piston which trap or are supplied with compressedair to provide an upwardly directed pneumatic bias for releasablyholding the piston in its normal position, this bias being removed assoon as the piston moves downwardly into the uniform diameter portion ofthe cylinder. The piston biasing air is derived directly from thereservoir air or from a valve carried on the piston.

20 Claims, 8 Drawing Figures t l i FASTENER DRIVING TOOL WITH IMPRIVEDPNEUMATIC PISTON RETAINING MEANS This invention relates to a pneumaticfastener driving tool using a brief pulse of pressurized fluid torestore a piston to a normal position, and more particularly, to such atool having new and improved means for releasably retaining the pistonin its normal position.

Many fastener driving tools use pneumatic piston return systems toobtain such advantages as the reduction of tool height and the removalof the need for a return spring. In some of these systems, the pistonand cylinder have different diameter portions effective over the entirestroke of the piston with the result that the piston must always bedriven through its power stroke in opposition to the return bias or elsethe volume bound by the different diameter portions must be great enoughto supply adequate air for returning the drive systemto a normalposition. Such prior arrangements using two separate cylinder portionsof different diameters are shown, for example, in US. Pat. Nos.3,040,709; 3,043,272; and 3,208,353. One such arrangement using acylinder continuously tapered from top to bottom is shown in US. Pat.No. 3,229,589.

In another type of air return system, such as shown in U.S. Pat. Nos.2,979,725; 3,l73,340; and 3,190,187, single-diameter cylinders andpistons are used, and valve arrangements are provided for supplying airbelow the piston to return the piston to normal position. In a variationof these arrangements, part of the air swept by the piston on its drivestroke is trapped or stored during the drive stroke, and this air withsome added air is used for return. Examples of this type of system areshown in US. Pat. Nos. Re. 26,262; 3,353,453; and 3,363,517. These typesof tools either require the provision of air beneath the piston to holdit in normal position between strokes or else require some mechanicalmeans or means independent of air pressure for holding the piston in itsnormal position. Some tools use the normal friction between the pistonO-ring and the cylinder wall. This friction may not be adequate if thetool is subjected to sharp blows. Other tools use mechanical latchessuch as magnets or spring-biased members which add parts to the tool andthus increase its cost.

Accordingly, one subject of the present invention is to provide a newand improved pneumatic fastener driving tool.

Another object is to provide a fastener driving tool with new andimproved pneumatic means for releasably holding a piston in its normalposition between strokes.

A further object is to provide a pneumatic means for releasably holdingin a normal position a piston which has been returned to this normalposition by a brief impulse of pressurized fluid, which pneumaticholding means do not retard movement of the piston through its power ordriving stroke.

Another object is to provide a pneumatic means for releasably holding apiston in normal position, which holding means does not requireadditional parts or space.

A further object is to provide a pneumatic means for releasably holdingin a normal position a piston returned to its normal position by a briefimpulse of pressurized fluid, which holding means uses the same valvearrangement used to supply at least a part of the pressurized pistonreturn fluid.

In accordance with these and many other objects, an embodiment of theinvention comprises a pneumatic fastener driving tool having a cylinderin which is slidably mounted a piston for actuating a fastener drivingblade or driver. A main valve assembly selectively connects the upperend of the cylinder to the atmosphere or to a reservoir or source ofpressurized fluid such as compressed air for driving the piston from anormal position at the upper end of the cylinder to a displaced positionat the lower end of the cylinder during which a fastener such as astaple or nail supplied below the driver is driven. When the upper endof the cylinder is connected to the atmosphere by the main valveassembly, a brief impulse of pressurized fluid supplied to the lower endof the cylinder below the piston, as from a return air storage chamberor by a valve, returns the piston from its displaced position to anormal position, the return air being dissipated to the atmosphere asand after the piston is returned to its normal position.

In accordance with the present invention, novel pneumatic means areprovided for retaining the piston and a connected driver blade in theirnormal positions in the interval between successive operating cycles orstrokes of the fastener driving tool. This pneumatic retaining meansincludes a two-diameter portion formed in the upper end of the cylinderin the area occupied by the piston in its normal position, The remaininginternal surface of the cylinder is of a uniform diameter. The pistonincludes a pair of O-rings which in the normal position of the pistonseal against the two-diameter portion. Pressurized fluid or compressedair is selectively supplied to an airreceiving space between the twosealing means and is retained therein between cycles of operation of thetool. This pressurized fluid acting on the different diameter portionsof the cylinder and the sealing means carried on the piston produce anupwardly directed pneumatic bias releasably retaining the piston in itsnormal position, When compressed air is supplied to the upper end of thecylinder to drive the piston downwardly, the sealing means on the pistonboth engage the uniform diameter portion of thelpiston, thereby removingthe differential areas and removing the bias so that the drive stroke ofthe piston takes place without requiring the piston to operate against areturn bias. A pressurized fluid can be supplied between the O-ringseither directly from the reservoir air or selectively under the controlof valve means carried on the piston which may be provided to supply theimpulse of compressed air for returning the piston to its normalposition. Thus, the releasable pneumatic piston holding means of thepresent invention does not require additional parts over and above thosenormally encountered in tools of this type, does not provide a returnbias operating against the piston during its power stroke, and affords apositive pneumatic bias supplying adequate force to maintain the pistonin its normal position between driving strokes, even when the tool issubjected to sharp blows.

Many other objects and embodiments of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which:

FIG. 1 is a fragmentary sectional view of a fastener driving toolembodying the improved pneumatic holding means of the present invention;

FIG. 2 is a sectional view of another embodiment of the pneumaticholding means used in the tool shown in FIG. 1;

FIG. 3 is a fragmentary sectional view of another embodiment ofapneumatic holding means useful with the tool shown in FIG. 1;

FIG. 4 is a fragmentary sectional view of a pneumatic fastener drivingtool embodying another form of a pneumatic piston holding means;

FIG. 5 is a fragmentary sectional view of another pistoncylinderarrangement embodying the novel pneumatic holding means of the presentinvention, which holding means is illustrated in conjunction with a toolof the type shown in FIG. 4; and

FIGS. 6, 7 and 8 are fragmentary sectional views of furtherpiston-cylinder modifications embodying the novel pneumatic holdingmeans.

Referring now more specifically to FIG. 1 of the drawings, therein isillustrated a fastener driving tool which is indicated generally as 10and which embodies the present invention. The tool 10 includes a housing12 having a forward and generally vertically extending head portion 12Aand a rearwardly extending hollow handle portion 12B forming a reservoir14 to which a pressurizedfluid, such as compressed air is supplied inany suitable manner, as by a flexible air line. The head portion 12A ofthe housing includes a cavity 16 in which is mounted a cylinder 18having its lower end in communication with the cavity I6 and an upperopen end in continuous communication with a passageway formed in thehousing. A control valve assembly which is manually controlled and whichis indicated generally as 22 normally connects the passageway 20 to theatmosphere through a passageway 24 formed in the hollow handle portion123, and this control valve assembly 22 is operable to a position inwhich it connects the passageway 20 to the reservoir 14. The fluidadmitted to the passageway 20 enters the open upper end of the cylinder18 and drives a piston 26 which is slidably mounted within the cylinder18 and which is secured to the upper end of a fastener driving blade 28downwardly so that the lower end of the blade engages and drives afastener supplied to a drive track in a nosepiece assembly 30 by amagazine assembly indicated generally as 32. Before the piston 26 canmove downwardly through a power stroke from its normal position shown insolid line in FIG. 1 to its displaced position shown in dashed outline,a pneumatic bias afforded by a releasable pneumatic holding meansindicated generally as 34 must be overcome.

As the piston 26 moves downwardly toward its displaced position shown indashed outline in FIG. 1, a portion of the air disposed beneath thepiston is discharged to the atmosphere through the structures definingthe drive track in the nosepiece structure 30 in the lower end of thehead portion 12A, and a portion of the air is forced into an air returnreservoir or space 36 formed in the cavity 16 between the walls of thehead portion 12A and the cylinder 18. A valve assembly on the piston 26supplies additional compressed air from above the piston 26 to the airreturn reservoir 36 when the piston 26 is in its displaced position.When the valve assembly 22 releases to interrupt the connection betweenthe passage 20 and the compressed air reservoir 14 and to connect thepassage 20 to the atmosphere through the exhaust passage 24, the upperend of the cylinder 18 is exhausted, and the compressed air stored inthe reservoir 36 enters the lower end of the piston 18 and provides amomentary impulse of pressurized fluid for restoring the piston 26 andthe connected driver blade 28 to the normal position illustrated inFIG. 1. When the piston 26 reaches the illustrated position, thepneumatic holding means 34 is rendered effective to pneumatically biasthe pist n to retain this position until the next operating cycle of thetool 10.

The general mechanical construction of the housing 12 and the magazineassembly 32 can be of any type well known in the art, such as theconstruction shown in US. Pat. No. 3,215,324. In general, the headportion 12A of the housing 12 includes a structure defining a circularopening in which a flange portion 18A of the cylinder 18 is receivedwith the interface between the wall of the head portion 12A and theouter wall of the flange portion 18A being sealed by an O-ring 44. Anupper opening in the head portion 12A is closed by a closure cap 46removably secured to the housing 12. A centrally disposed opening 48 inthe upper surface of the piston 26 carries a resilient or elastic bumper50 which engages the lower wall of the closure cap 46 to provide aresilient stop for arresting return movement of the piston 26 in itsnormal position. Another cylindrical or annular resilient or elasticbumper 52 is disposed in the lower end of the cavity 16 adjacent thelower end of the cylinder 18 to provide a means for arresting downwardmovement of the piston 26 at the end of its power stroke. The lower endof the interior of the cylinder 18 is placed in communication with theair return space 36 through two axially spaced sets of ports 54 and 56.

The piston 26 carries a pair of axially spaced, expansible, andcompressible sealing means or O-rings 58 and 60 which individually orconjointly not only seal the interface between the cylinder 18 and thepiston 26, but also form part of the pneumatic holding means 34 andcontrol the admission of pressurized fluid or compressed air to the airreturn space or reservoir 36. The O-ring 60 is mounted in a peripherallyextending groove on the piston 26,. and the O-ring 58 is mounted in aperipherally extending groove in which one or a plurality of slots orrecessed portions 62 are provided. The O-ring S8 cooperates with thegroove in which it is disposed and the slots 62 in the manner describedin detail in US. Pat. No. 3,040,709 to provide a one-way check valvewhich permits pressurized fluid to flow from above the O-ring 58 to thearea disposed between the O-rings 58 and 60 and to prevent the flow ofpressurized fluid from this space to the area above the O-ring 58.

As indicated above, the control valve assembly 22 controls thereciprocation of the piston 26 within the cylinder 18 by selectivelyconnecting the upper end of this cylinder or the passageway 20 to eitherthe pressurized fluid reservoir 14 or the passageway 24 extending to theatmosphere. The construction of the valve 22 is illustrated anddescribed in detail in U.S. Pat. No. 3,173,340. In general, the valveassembly 22 includes a pilot valve assembly indicated generally as 66which is actuated by manual operation of a trigger 68 to controlmovement of a main valve assembly 70 between normal and actuatedpositions, the valve assembly 22 being shown in a normal position inFIG. 1. The valve assembly 70 includes a resilient sealing element orO-ring 72 which is selectively moved into and out of engagement with avalve seat 74 forming a tapered throat to selectively place thepassageway 20 into and out of communication with the exhaust passageway24. The valve assembly 70 also includes another resilient sealing orvalve element 76 which is selectively moved into and out of engagementwith structure defining a port 78 to place the passageway 20 in and outof communication with the pressurized fluid reservoir 14.

When the tool 10 is to be operated, the trigger 68 is actuated tocontrol the pilot valve assembly 66 so that the main valve assembly 70moves downwardly from the position illustrated in FIG. 1 so that theresilient valve 72 seats on the valve seat 74, and the valve element 76moves out of engagement to open the port 78. The valve element 72 closesoff communication between the passage 20 and the exhaust passageway 24,and the opening of the port 78 supplies pressurized fluid from thereservoir 14 through the passageway 20 to the open upper end of thecylinder 18. The compressed air supplied to the upper surface of thepiston 26 at the open upper end of the cylinder 18 overcomes the holdingforce provided by the assembly 34 and drives the piston 26 downwardlythrough a power stroke from its illustrated normal position to thedisplaced position illustrated in dashed outline. During this movement,the O-rings 58 and 60 seal the interface between the cylinder 18 and thepiston 26 so that the pressurized fluid supplied to the top of thecylinder 18 is effective to drive the piston 26 downwardly and actuatethe blade 28 to drive and set a fastener supplied to the drive track inthe nosepiece structure 30 by the magazine assembly 32. During thisdownward movement, a portion of the air beneath the piston 26 isdischarged to the atmosphere, and a portion of this air is suppliedthrough the ports 54 and 56 to the air return space or reservoir 36.

When the piston 26 reaches its displaced position, further downwardmovement of the piston is arrested by engagement with the bumper 52. Atthis time, compressed air within the cylinder 18 above the piston 26acts on the upper O-ring 58 to move this O-ring somewhat downwardlywithin the groove within which it is mounted so that air passing throughthe interface between the cylinder 18 and the piston 26 above the O-ring58 passes through the slots or recesses 62 and through the upper ports56 to be accumulated within the return air space 36. A portion of thisair is also disposed in an air receiving space defined by the area ofthe interface between the axially spaced O-rings 58 and 60. The piston26 remains in its displaced position until the control valve assembly 22is released.

At this time, the release of the trigger 68 permits the pilot valveassembly 66 to return to its normal position so that the main valveassembly 70 returns to the normal position illus' trated in FIG. 1. Thiscloses the port 78 and moves the valve element 72 out of engagement withthe valve seat 74 so that pressurized fluid or compressed air within thecylinder 18 above the piston 26 is discharged to the atmosphere throughthe passageway 24. This produces a pressure differential across theO-ring 58 so that it moves to an upper position closing offcommunication through the slots or recesses 62 between the area sealedby the O-rings 58 and 60 and the portion of the cylinder 18 disposedabove the O-ring 58. At this time, compressed air in the reservoir 36enters the lower end of the cylinder 18 through the ports 54 and movesthe piston 26 upwardly until such time as the bumper 50 engages thelower surface of the closure cap 46, in which position the piston 26occupies its normal position. As the piston 26 moves into this normalposition, the pneumatic holding means 34 are rendered effective.

More specifically and in order to provide the pneumatic holding means34, the inner surface of the upper end of the cylinder 18 is providedwith a greater diameter portion 18B, the diameter of which is greaterthan the uniform diameter of the remaining portion of the interiorsurfaces of the cylinder 18. The greater diameter portion 18B occupiesan axial length no greater than the spacing between the O-rings 58 and60. As the piston 26 was moved upwardly from its displaced positiontoward the normal position shown in FIG. 1, the lower O-ring 60 sealedoff the port 56 so that pressurized fluid is trapped between the O-rings58 and 60. This pressurized fluid is carried upwardly with the piston 26as it moves to its normal posi tion. When the piston 26 reaches itsnormal position, the upper O-ring 58 expands outwardly to maintain itssealing engagement with the inner surface of the cylinder 18 and therebyproduces an arrangement of differential areas exposed to the pressurizedfluid trapped between the O-rings 58 and 60. More specifically, as theupper O-ring 58 expands into the greater diameter portion 18B of thecylinder 18, the piston 26 is provided with a greater diameter upperportion which the compressed air trapped between the O-rings 58 and 60acts on to provide an upwardly directed component of force urging thebumper 50 on the piston 26 against the stop surface provided by thelower wall of the closure cap 46, This force dependent on the compressedair trapped between the O-rings 58 and 60 provides a continuous upwardlydirected bias positively holding the piston 26 in its normal position asthe return air leaks to the atmosphere from the cylinder 18 below thepiston.

The advantages of the pneumatic holding means 34 are many. In the firstplace, any blows applied to the tool which tend to move the piston 26downwardly thereby cause the compression of the volume of pressurizedfluid trapped between the O-rings 58 and 60 so that a greater upwardlydirected biasing force is generated. This greater force tends toovercome the forces which would inadvertently cause downward movement ofthe piston 26. In the second place, once the pneumatic retention of thepiston 26 provided by the assembly 34 is overcome during normaloperation of the tool, the piston 26 moves downwardly through its powerstroke without any opposing bias. More specifically, this is truebecause as the O-ring 58 enters the lesser or uniform diameter portionof the cylinder 18 immediately after the piston 26 starts its downwardmovement, this O-ring is compressed to the same effective diameter asthe lower O-ring 62 and the piston 26 is no longer provided withdifferential areas exposed to the entrapped pressurized fluid. Thus, thenet force acting on the piston 26 from the entrapped fluid is zero, andthe full force of the pressurized fluid admitted to the top of thecylinder 18 is effective to drive the piston 26 downwardly. A furtheradvantage of this arrangement is that the pneumatic holding means 34 canbe achieved without requiring any additional parts merely by increasingthe diameter of the portion 188 of the cylinder 18. The O-rings 58 and60 are normally provided to seal the piston-cylinder interface and toafford means for supplying additional compressed air to the reservoir 36at the end of the power stroke. These same components provide means forsupplying the small quantity of corripressed air that is trapped betweenthe O-rings 58 and 60 to provide the upwardly directed bias when thepiston is in its normal position.

Referring now more specifically to FIG. 2 of the drawings, therein isillustrated a pneumatic fastener driving tool which is indicatedgenerally as 70 and which embodies the present invention. The tool 70is, in most respects, identical to the tool 10 except for a modificationin the construction of a piston 72 and a return bumper 74 carriedthereon. This similarity or identity of parts is indicated by the use ofidentical reference numbers. The modifications provide a pneumaticholding means indicated generally as 76 for the piston 72 which issimilar in operation and construction to the pneumatic holding means 34provided for the tool 10.

More specifically, the piston 72 is of generally the same configurationas the piston 26 and is secured at its lower end to the upper end of thedriver blade 28, the piston 72 being slidably mounted within thecylinder 18. However, the piston 72 is provided with two similar groovesor recesses for receiving the two O-rings 58 and 60 so that the O-ring58 no longer provides the additional function of providing a check valveconstruction.

To provide the check valve for both supplying entrapped air for use inthe pneumatic holding means 76 and for supplying pressurized fluid tothe return air space 36 through the ports 56, the piston 72 is providedwith a peripherally extending recessed area 78, the inner portion ofwhich is in communication with a plurality of peripherally spaced andradially ex tending passageways which open into the opening 48 in whichthe resilient bumper 74 is seated. The lower end of the bumper 74 isprovided with a plurality of passageways 74A which place the passageways80 in communication with the pressurized fluid supplied by thepassageway 20 through an axially extending opening 74B in the bumper 74.A circular or annular resilient O-ring or valve element 82 is seated inthe groove 78 and normally seals the outer ends of the radial passages80.

Accordingly, when the control valve assembly 22 is actuated to supplycompressed air to the passageway 20, the pneumatic holding forceprovided by the assembly 76 is overcome. and the piston 72 is drivendownwardly to its displaced position determined by engagement'of thelower surface of the piston 72 with the resilient bumper 52. At thistime, compressed air passes through the passageways or openings 74B, 74Aand 80 to unseat the circular valve element 82. Thus, pressurized fluidis supplied through the port 56 to the return air space 36 and to thearea in the interface between the 0- rings 58 and 60 defined thereby.When the passageway 20 is connected to the atmosphere, pressurized fluidin the reservoir return space 36 is supplied to the lower end of thecylinder 18 beneath the piston 72 through the ports 54, and the piston72 is returned to the normal position illustrated in FIG. 2. Further,when the upper end of the cylinder 18 is connected to the atmosphere,the O-ring 82 seals the radial passageways 80 so that when the O-ring 60passes the ports 56, a body of pressurized fluid is trapped between theO-rings 58 and 60.

When the piston 72 reaches its upper or normal position defined byengagement of the bumper 74 with the closure cap 46, the O-ring 58expands out to sealing engage ment with the greater diameter portion 18Bof the cylinder, and the pressurized fluid trapped between the O-rings58 and 60 expands in the area of volume therebetween and acts on theeffective greater diameter upper portion of the piston 72 afforded bythe expanded O-ring 58. This provides a continuous upwardly directedbias holding the bumper 74 against the closure cap 46 to pneumaticallybias and retain the piston 72 in its normal position. As with thepneumatic holding means 34, the means 76 does not offer any resistanceto downward movement of the piston 72 after the O-ring 58 clears thegreater diameter portion 183 of the cylinder 18 and requires noadditional parts while affording a positive holding force for retainingthe piston 72 in its normal position.

FIG. 3 of the drawings illustrates a tool indicated generally as whichembodies the present invention and which is identical to the tool 10except for the construction of a cylinder 92. The identity of the partsis designated by the use of identical reference numbers forcorresponding parts. The modified cylinder 92 cooperates with the piston26 to provide a pneumatic holding means indicated generally as 94 whichis identical in function and operation to the holding means 34.

More specifically, the cylinder 92 is identical to the cylinder 18except that the upper end of the cylinder 18 is provided with anoutwardly flared or tapered upper end portion 92B. The tapered wallsection 92B is engaged by the O-rings 58 and 60 when the piston 26 is inthe normal position shown in FIG. 3, and thus affords different diameterportions on the piston 26 and the cylinder 92 which result in a netupwardly directed pneumatic bias acting on the piston 26 to retain it inits normal position. The advantage of the tapered wall 928 in place ofthe stepped wall of the cylinder 18 where the greater diameter portion18B is formed arises from the fact that there may be somewhat less wearon the upper O-ring 58 with the tapered wall 92B. This is true becauseas the piston 26 moves downwardly, the O-ring 58 is compressed by agradual camming rather than an abrupt camming action, as with thecylinder 18. The tapered wall can also be used at the upper end of thecylinder 18 in the tool 70 illustrated in FIG. 2.

FIG. 4 of the drawings illustrates a pneumatic fastener driving toolwhich is indicated generally as 100 and which embodies the presentinvention. The tool 100 is similar in operation to the tools 10, 70, and90 insofar as a piston 102 is reciprocated within a cylinder 104 betweennormal and displaced positions to actuate a driver blade 106 connectedto the piston 102 so as to drive a fastener supplied to a drive track ina nosepiece structure 108 from a magazine 110. The tool 100 differs,however, from the tools 10, 70, and 90 in the respect that pressurizedfluid or compressed air from a reservoir 112 formed in a hollow handleportion 114A ofa housing 114 is continuously present in an areasurrounding the upper end of the cylinder 104, as contrasted with thetools described above in which pressurized fluid is supplied to aposition in proximity to the upper input of the cylinder through a valveand reservoir located somewhat remote from the cylinder 104. Thismodification in the driving system or the control for the driving systemfor the piston 102 in the tool 100 makes possible the provision ofanother modified form of the pneumatic piston holding means which isindicated generally as 1 16.

The drive system for and the construction of the tool 100 is illustratedand described in detail in the copending application of Richard H.Doyle, Ser. No. 602,728, filed Dec. 19, 1966. Only slight modificationshave been made in the piston 102 and the cylinder 104 to make possiblethe provision of the improved pneumatic holding means 1 16 in the tool100.

As set forth in detail in the above-identified and copending Doyleapplication, compressed air from the reservoir 112 in the normalcondition of the tool 100 passes by a ball valve 117 and over a seriesof passageways 118 to be applied to the greater area upper surface of acombined main valve-exhaust valve assembly indicated generally as 120,the compressed air supplied by the passageway system 118 being disposedin a chamber 122. This pneumatically biases a resilient diaphragm 124 inthe assembly 120 against the open upper end of the cylinder 104 so as toseal off communication between the compressed air surrounding the openupper end of the cylinder 104 and the interior thereof.

When the tool 100 is to be operated, a trigger 126 is depressed so thatan actuating element 128 secured to the ball valve 117 moves upwardly tomove this ball valve upwardly. This disconnects the passageway system118 from the reservoir 112 and connects it to the atmosphere through anopening which is normally sealed by engagement of the ball valve 117with an O-ring 130. This discharges the air from the chamber 122 to theatmosphere and permits the pressurized fluid acting on the lower surfaceof the diaphragm 124 to move the main valve assembly 120 upwardly. lnmoving upwardly, the upper surface of an exhaust valve stem 132 movesinto seating engagement with a resilient exhaust valve element 134 toclose off communication through an axial passage 136 in the stem 132between the upper interior of the cylinder 104 and the atmosphere. Theupward movement of the valve assembly and of the diaphragm 124 admitspressurized fluid from the reservoir 112 to the top of the interior ofthe cylinder 104 so that the piston 102 moves downwardly through a powerstroke which is terminated by engagement of the piston 102 with aresilient bumper 138. The interface between the piston 102 and thecylinder 104 is sealed by two axially spaced resilient or expansiblesealing means or O-rings 140 and 142.

When the piston 102 reaches its displaced or lower position, compressedair from within the cylinder 104 above the piston 102 passes through aplurality of radially extending passageways 144 in the piston to unseata resilient valve element or O-ring 146 so that this compressed airpasses through a plurality of peripherally spaced ports 148 in the lowerend of the cylinder 104 to be collected together with air swept by thepiston 102 during its power stroke in an air return space or reservoir150.

When the trigger 126 is released, pressurized fluid in the reservoir 112biases the ball valve 117 downwardly into engagement with the O-ring toclose off the connection between the passageway system 118 and theatmosphere. At the same time, compressed air from the reservoir 112enters the passageway 1 18 and flows into the chamber 122. Thepressurized fluid in the chamber 122 when combined with the downwardlydirected force of a compression spring 152 moves the valve assembly 120downwardly so that the diaphragm 124 seats on the upper end of thecylinder 104 to close off communication between the pressurized fluidand the interior of the upper end of the cylinder 104. At the same time,the upper end of the valve stem 132 moves downwardly out of engagementwith the exhaust valve element 134 so that the interior of the cylinder104 above the piston 102 is connected to the atmosphere through thepassageway 136. At this time, the valve element 146 seals the radialpassageways 144, and the compressed air in the air return space entersthe lower end of the interior of the cylinder 104 through the ports orpassageways 148. This compressed air moves the piston 102 upwardly toits normal position illustrated in FIG. 4. This position is determinedby engagement of the upper surface of the piston 102 with the lowersurface of the diaphragm 124 in the main valve assembly 120.

The pneumatic holding means 116 retains the piston 102 in this normalposition until the next cycle of operation of the tool 100. It isnecessary to provide this pneumatic holding means because the compressedair supplied from the reservoir becomes dissipated by leakage to theatmosphere between operations of the tool, such leaking occurring, forinstance, along the driver blade 106 and at other places. The pneumaticholding means 116 includes a greater diameter portion 104A formed in theupper end of the cylinder 104 in only the part thereof occupied by thepiston 102 in its normal position, the remaining interior surface of thecylinder 104 being of substantially uniform diameter somewhat less invalue than the greater diameter portion 104A. The greater diameterportion 104A is so located that as the piston engages the stop providedby the diaphragm 124, the lower O-ring 142 remains in sealing engagementwith the uniform lesser diameter portion of the interior surface of thecylinder 104, and the upper O-ring 140 expands into sealing engagementwith the greater diameter portion thereby defining a dual diameterpiston and cylinder relationship. The upper end of the cylinder 104 isprovided with a port or passage 154 extending between the pressurizedfluid in the reservoir 112 and the portion of the interior of thecylinder 104 disposed between the O-rings 140 and 142. Accordingly, whenthe piston 102 reaches the normal position illustrated in FIG. 4, thepressurized fluid is supplied between the O-rings 140 and 142 and actson the effective differential diameters of the piston 102 to provide acontinuous upwardly directed pneumatic bias holding the upper surface ofthe piston 102 against the stop afforded by the diaphragm 124.

Thus, the pneumatic piston retaining or holding means 116 included inthe tool 100 also provides means for pneumatically retaining in itsnormal position the piston 102 while permitting this piston 102 to bedriven downwardly free of the effects of a return bias. in the holdingmeans 116, the pressurized fluid acting on the differential diameters ofthe piston 102 is supplied directly from the reservoir 112 in the normalposition of the piston 102, and no means are required on the piston 102for entrapping this fluid, as in the constructions illustrated in FIGS.1, 2, and 3. If desired, the greater diameter portion 104A of thecylinder 104 can be fonned with a tapered surface comparable to thetapered surface 92B provided on the upper end of the cylinder 92 in thetool 90 illustrated in FIG. 3 of the drawings.

FIG. 5 of the drawings illustrates a tool 160 which in its generalconstruction is identical to the tool 100 in including a pneumaticholding means 116. To illustrate the identity of parts, identicalreference numbers have been applied to the same parts in FIGS. 4 and 5.

The tool 160 differs from the tool 100 in the manner of supplyingpressurized fluid to the air return space 150. More specifically, theradial passageways 144 and the O-ring 146 have been removed from thepiston 102 in the tool 160, and the cylinder 104 has been provided witha plurality of spaced ports 162 adjacent its lower end, which ports 162are normally closed by a resilient valve element or O-ring 164.

When the piston 102 is driven to its displaced position engaging thebumper 138, the upper end of the piston 102 clears the ports 162, andthe pressurized fluid in the upper end of the cylinder 104 displaces theO-ring 164 to permit the pressurized fluid to be accumulated within thechamber 150. This fluid returns the piston 102 to its normal conditionwhen the upper end of the cylinder 104 is connected to the atmosphere inthe manner described above. This connection of the upper end of theinterior of the cylinder 102 to the atmosphere permits the O-ring 164 toseat and again close the ports 162. When the piston 102 is returned toits normal position, pressurized fluid supplied from the reservoir 112through the ports 154 to the area bounded by the O-rings 140 and 142again effects the resilient bias of the piston 102 to its normalposition determined by engagement with the lower surface of thediaphragm 124.

FIG. 6 of the drawings illustrates a pneumatic holding means indicatedgenerally as 170 which embodies the present invention and which isuseful, for instance, in a tool such as that illustrated in FIG. 5. Thepneumatic holding means 170 includes a cylinder 172 having a greaterdiameter portion 172A at its upper end in the area normally occupied bya piston 174 when this piston is in its illustrated normal position. Thepiston 174 is coupled, for example, to a driver blade (not shown).

The holding means 170 includes a pair of resilient and expansiblesealing means or O-rings 176 and 178. The O-ring 176 is carried in arecess or groove adjacent the top of the piston 174 and is adapted toseal the interface between the piston 174 and the cylinder 172 as thepiston 174 moves through its drive or power and return strokes. Thesealing means or O-ring 178, however, is disposed within a recess orgroove 1728 on the inner surface of the cylinder 172 and seals theinterface between the piston 174 and the cylinder 172 only when thepiston 174 is in the normal position illustrated in FIG. 6. Thus, duringthe power stroke the interface between the cylinder 172 and the piston174 is sealed only by the sealing means 176.

When the piston 174 is returned to its normal position illustrated inFIG. 6, the upperO-ring 176 expands outwardly in a radial direction toengage the wall surface of the greater diameter Portion 172A of thecylinder 172 and to provide an upper seal. At the same time, the lowerportion of the piston 174 moves into a sealing engagement with theO-ring 178 carried on the cylinder 172 to define a lower seal.Compressed air supplied through a port or opening 180 enters the areabound by the two sealing means 176 and 178 and provides an upwardlydirected pneumatic bias acting on the greater diameter effectivestructure of the piston 174 to bias this piston upwardly against asuitable stop structure (not shown). Thus, the piston 174 ispneumatically retained in its normal position by the assembly with onlya single sealing means 176 carried on the piston 174.

HO. 7 illustrates a pneumatic holding means which is indicated generallyas 190. The assembly or holding means includes a cylinder 192 in whichis slidably mounted a piston 194. The piston 194 carries a pair ofexpansible or resilient sealing means or O-rings 196 and 198. The upperend of the cylinder 192 is provided with an undercut portion 192Aagainst which the upper sealing means 196 seals when the piston 194 isin its normal position.

The holding means 190 can be used, for example, in a tool such as thetool 10 by providing structure so that the upper sealing means 196operates as a one-way check valve, such as the O-ring 58, in addition toits normal sealing function. In this application, the area between theO-rings 19 6 and 198 is supplied with pressurized fluid under thecontrol of the check valve action afforded by the O-ring 196. Thus, whenthe piston 194 is returned to its normal position illustrated in FIG. 7,the sealing engagement of the O-ring 196 with the greater diameterportion of the cylinder 192 provided by the undercut portion 192Aresults in an upwardly directed pneumatic biasing force which holds thepiston 194 against a stop (not shown) in its normal position.

On the other hand, if the holding means 190 is to be used in a tool suchas that illustrated in FIG. 5, the O-rings 196 and 198 provide seals forthe interface between the piston 194 and the cylinder 192 and do notprovide the function of supplying pressurized fluid for either thepneumatic holding means or the piston return system. In thisapplication, a port or passage 200 communicating with pressurized fluidis provided in the cylinder 192 communicating with the undercut portion192A. The passage 200 supplies pressurized fluid which acts on theeffective greater diameter upper structure on the piston 194 to bias thepiston to its normal position.

The pneumatic holding means can also be constructed using a cylinder ofagiven diameter which is uniform along its length except for a portion oflesser diameter in the area engaged by the lower O-ring or sealing meanswhen the piston is in its normal position to provide the differentialpiston and cylinder diameters.

FIG. 8 of the drawings illustrates a further embodiment 210 of thepneumatic holding means which is useful, for example, in the tool 10.The construction of a tool incorporating the holding means 210 is thesame as that of the tool 10 except for the arrangement ofthe pistonsealing means. Accordingly, like reference numbers are used in FIGS. 1and 8 to designate identical parts.

It has been determined in operating the tool 10 that, on occasion,insufficient compressed air or pressurized fluid is trapped between thesealing means 58 and 60 to effect as positive a holding force as wouldbe desired. It has been further determined that the fluid available forholding can be increased by using the lower O-ring 60 as a one-way checkvalve. Accordingly, the piston 26 is provided with slots or recesses 62Ain the groove for the O-ring 60 so that this O-ring provides a checkvalve similar to the O-ring 58. The check valve provided by the O-ring60 will not pass fluid from above this O-ring to below this O-ring butwill pass air from below this O-ring to above this O-ring In operatingthe tool 10 with the holding means 210, the pressurized fluid admittedto the cylinder 18 drives the piston 26 downwardly and suppliescompressed air to the reservoir 36 through the opening 56 in the mannerdescribed above. The air passing the check valve afforded by the O-ring58 does not pass the O-ring 60 because this O-ring closes the slots 62Aduring the power stroke.

During the return stroke, the O-ring 58 seals the slot 62 when the topof the cylinder 18 is vented to the atmosphere. Pressurized fluid fromthe reservoir 36 enters the lower end of .7 1L the cylinder 18 throughthe opening 54 to move the piston 26 upwardly. Part of the air alsopasses back to the area between the O-rings 58 and 60 through theopening 56, which area is sealed when the O-ring 60 passes beyond theopening 56. If insufficient air is trapped between the O-rings 58 and60, the air in the cylinder 18 below the O-ring 60 unseats the O-ring tomomentarily open the slots 62A so that compressed air from below theO-ring 60 passes into and is trapped in the fluid receiving spacebetween the O-rings 58 and 60. The O-ring 60 closes the slots 62A whenthe pressure below this O-ring drops as by leakage to the atmosphere.This supplemental holding air insures positive retention of the piston26 in its normal position.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. In a fastener driving tool of the type using an impulse ofpressurized fluid for returning a piston from a displaced position to anormal position in which the piston is to be retained, said pistonhaving a single effective diameter during its movement between saiddisplaced and normal positions, said single effective diameter beinglocated at an upper portion of said piston,

a cylinder in which the piston is slidably mounted, said cylinder havinga first end portionoccupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having at its type using an impulse of a pressurized fluidfor returning a piston from a displaced position to a normal position inwhich the piston is to be releasably retained, said piston having asingle effective diameter during its movement between said displaced andnormal positions, said single effective diameter being located at anupper portion of said piston,

a cylinder in which the piston is slidably mounted, said cylinder havinga first end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position an inner wall surface with greater andlesser diameter portions, the remaining inner surface of the cylinder insaid intermediate portion being of a substantially uniform diametergenerally corresponding to said single diameter said cylinder havingport means at said second end portion,

a pair of spaced sealing means on the piston slidably engaging the innerwall surface of the cylinder and defining a fluid-receiving spacetherebetween, at least one of the sealing means being expansible andcompressible,

an air return space communicating with the interior of the cylinder atthe second end portion through the port means,

first stop means for arresting movement of the piston in said displacedposition with the piston adjacent the port means,

return means for providing pressurized fluid to said air return spacewhich passes through said port means to provide said impulse ofpressurized fluid to return the piston to its first end portion andspaced from an intermediate portion of the cylinder through which thepiston moves in moving to the displaced position an inner wall surfacewith greater and lesser diameter portions, the remaining inner surfaceof the cylinder in said intermediate portion being of a substantiallyuniform diameter generally corresponding to said single diameter,

a pair of spaced sealing means on the piston slidably engaging the innerwall surface of the cylinder and defining a fluid receiving spacetherebetween, at least one of the sealing means being expansible andcompressible,

piston return means for supplying an impulse of pressurized fluid forreturning the piston from the displaced position to the normal position,

stop means on the tool for arresting return movement of the piston inthe normal position with the pair of spaced sealing means engaging thedifferent diameter portions of the inner wall surface of the cylinder,

and air-supplying means for supplying pressurized fluid to said spacebetween the pair of sealing means which is effective by virtue of thedifferent diameter portions of the inner wall surface of the cylinderand the corresponding different effective diameters of the sealing meansto provide a fluid bias urging the piston toward the stop means whichreleasably retains the piston at the first end of the cylinder in itsnormal position.

2. The fastener driving tool set forth in claim 1 in which the cylinderhas a step formed in the inner wall surface to provide the greater andlesser diameter portions.

3. The fastener driving tool set forth in claim 1 in which the cylinderhas a tapered inner wall surface providing the greater and lesserdiameter portions.

4. The fastener driving tool set forth in claim 1 in which theair-supplying means includes valve means carried on the piston.

5. The fastener driving tool set forth in claim 4 in which the valvemeans includes the sealing means disposed adjacent the greater diameterportion of the inner wall surface of the cylinder when the piston is inits normal position.

6. The fastener driving tool set forth in claim 1 in which theair-supplying means includes a fluid pressure supplying passage passingthrough the cylinder and opening into the cylinder at said first endportion.

7. The fastener driving tool set forth in claim 1 in which theair-supplying means includes a unidirectional valve communicating withsaid space at one end and the interior of the cylinder above the pistonat the other end.

8. In a fastener driving tool of the normal position,

second stop means on the tool for arresting return movement of thepiston in the normal position with the pair of spaced sealing meansengaging the different diameter portions of the inner wall surface ofthe cylinder,

and air-supplying means for supplying pressurized fluid to said spacebetween the pair of sealing means which is effective by virtue of thedifferent diameter portions of the inner wall surface of the cylinderand the corresponding different effective diameters of the sealing meansto provide a fluid bias urging the piston toward the stop means whichreleasably retains the piston at the first end of the cylinder in itsnormal position, the pressurized fluid from said air return space beingexhausted to the atmosphere when the piston is returned to its normalposition.

9. The fastener driving tool set forth in claim 8 in which the returnmeans includes means controlled by the piston for supplying air to theair return space when the piston is in its displaced position.

10. The fastener driving tool set forth in claim 8 in which the returnmeans includes a valve carried on the piston for supplying pressurizedfluid to the air return space.

11. The fastener driving tool set forth in claim 8 in which a valvecarried on the piston forms a part of both the return means and theair-supplying means for supplying pressurized fluid to both the airreturn space and the fluid receiving space.

12. A fastener driving tool as set forth in claim 8 in which theair-supplying means includes a passage through the first end portion ofthe cylinder communicating with the fluidreceivmg space.

13. A fastener driving tool as set forth in claim 8 in which a fluidpressure reservoir continually supplied with pressurized fluid isdisposed adjacent the first end portion of the cylinder,

and the fluid-supplying means includes a passage through the first endportion of the cylinder between the reservoir and the fluid receivingspace.

14. In a fastener driving tool of the type in which a piston isreciprocated between a normal position in which the piston is to bereleasably retained and a displaced position, said piston having asingle effective diameter during its movement between said normal anddisplaced positions,

a cylinder in which the piston is slidably mounted, said cylinder havinga first end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having only at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position a part of its inner wall surface withgreater and lesser diameter portions,

stop means on the tool for arresting return movement of the piston inthe normal position,

a pair of spaced sealing means sealing the piston-cylinder interfacewhen the piston is in said normal position and defining afluid-receiving space therebetween, the pair of sealing means being sospaced as to provide seals at the different diameter portions of theinner wall surface of the cylinder, at least one of the sealing meansbeing carried on the piston and being expansible to different diametersto slidably engage the inner wall of the cylinder during thereciprocating movement of the piston,

and air-supplying means for supplying pressurized fluid to the spacebetween the pair of sealing means which is effective by virtue of thedifferent effective diameters of the piston to provide a fluid biasurging the piston toward the stop means which releasably retains thepiston at the first end portion of the cylinder in its normal position.

15. The fastener driving tool set forth in claim 14 in which the othersealing means is carried on the cylinder at its first end portion toengage the piston only when the piston is in its normal position.

16. The fastener driving tool set forth in claim 14 in which thecylinder has a substantially uniform diameter equal to said lesserdiameter,

and the greater diameter portion at said first end portion of thecylinder is formed by an undercut portion spaced slightly below the endof the cylinder.

17, The fastener driving tool set forth in claim 14 in which theair-supplying means includes a passage extending through the wall of thecylinder and supplied with pressurized fluid.

18. In a fastener driving tool of the type in which a piston isreciprocated between a normal position in which the piston is to bereleasably retained and a displaced position, said piston having asingle effective diameter during its movement between said normal anddisplaced positions,

a cylinder in which the piston is slidably mounted, said cylinder havinga first end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position a part of its inner wall surface withgreater and lesser diameter portions,

stop means on the tool for arresting return movement of the piston inthe normal position,

a pair of spaced sealing means sealing the piston-cylinder interfacewhen the piston is in said normal position and defining afluid-receiving space therebetween, the pair of sealing means being sospaced as to provide seals'at the different diameter portions of theinner wall surface of the cylinder, at least one of the sealing meansbeing carried on the piston and being movable between a first diameteronly when the piston is in said normal position and a second differentand constant diameter to slidably engage the inner wall of the cylinderduring the reciprocating movement of the piston through saidintermediate portion of the cylinder, first means for supplyingpressurized return fluid below the piston to move the piston from itsdisplaced position to its normal position,

and second means for supplying a part of said pressurized return fluidto the space between the pair of sealing means which is effective byvirtue of the different effective diameters of the piston to provide afluid bias urging the piston toward the stop means which releasablyretains the piston at the first end portion of the cylinder in itsnormal position.

19. The fastener driving tool set forth in claim 18 in which both of thesealing means are carried on the piston,

and the sealing means that engages the lesser diameter portion of thecylinder provides a check valve in said second means for supplying apart of the pressurized return fluid fggggg UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,638,534 Dated February 1,1972

Inventor(s) Howard B. Ramspeck It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below;

r- In place of Column 11, lines 16-72 and Column 12, 1

lines 1-12, insert the following claim:

-l. In a fastener driving tool of the type using an impulse ofpressurized fluid for returning a piston from a displaced position to anormal position'in which the piston is to be retained, said pistonhaving a single effective diameter during its movement between saiddisplaced and normal positions, said single effective diameter beinglocated at an ,upper portion of said piston,

a cylinder in which the piston is slidably mounted, said cylinder havinga first end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position an inner wall surface with greater andlesser diameter portions, the remaining inner surface of the cylinder insaid intermediate portion being of a substantially uniform diametergenerally corresponding to said single diameter,

a pair of spaced sealing means on the piston slidably engaging the innerwall surface of the cylinder and defining a fluid receiving spacetherebetween, at least one of the sealing means being expansible andcompressible,

' piston return means for supplying an impulse of pressurized fluid forreturning the piston from the displaced position to the normal position,

stop means on the tool for arresting return movement of the piston inthe normal position with the pair of l. t t J (page 1 of 3 pages) mg?UNITED STATES PATENT OFFICE CERTIFICATE OF fiORRECTION Patent No.3,638,534 4 Dated February 1, 1972 Inventor( s) Howard B. Ramspeck It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

spaced sealing means engaging the different diameter portions .1

of the inner wall surface of the cylinder,

and air supplying means for supplying pressurized fluid to said spacebetween the pair of sealing means which is effective by virtue of thedifferent diameter portions of the inner wall' surface of the cylinderand the corresponding different effective diameters of the sealing meansto provide a fluid bias urging the piston toward the stop means whichreleasably retains the piston at the first end of the cylinder in itsnormalpositionw- I In place of Column 12, lines 35-49, insert thefollowing claim:

--8. In a fastener driving tool of the type using an impulse of apressurized fluid for returning a piston from a displaced position to anormal position in which the piston is to be releasably retained, saidpiston having a single effective diameter "during its movement betweensaid displaced and normal positions, said single effective diameterbeing located at an upper portion of said piston,

' a cylinder in which the piston is slidably mounted, said cylinderhaving a first end portion occupied by the piston in its normal positionand a second end portion occupied by the piston in its displacedposition, said cylinder having at its first end portion and spaced froman intermediate portion of the cylinder through which the piston moves'in moving to the displaced position an inner wall surface with greaterand lesser diameter portions, the remaining inner surface of thecylinder in said intermediate (page 2 of 3 pages) "222 33 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,638, 534 DatedFebruary 1, 1972 lnventoi-(s) Howard B. 'Ramspeck It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

' portion being of a substantially uniform diameter generally .1

corresponding to said single diameter, said cylinder having port meansat said second end portion,

a pair of spaced sealing means on the piston slidably engaging the innerwall surface of the cylinder and defining a fluid receiving spacetherebetween, at least one of the sealing means being expansible andcompressible,

an air return space communicating with the interior. of the cylinder atthe second end portion through the port means, g I

first stop means for arresting movement of the piston in said displacedposition with the piston adjacent the port means,

return means for providing pressurized fluid to said air return spacewhich passes through said port means to provide said impulse ofpressurized fluid to return the piston to its normal position,

second stop means on the tool for arresting return movement of thepiston in the normal position with the pair of spaced sealing meansengaging the different diameter portions of the inner wall surface ofthe cylinder,

and air supplying means for supplying pressurized fluid to said spacebetween the pair of sealing means which is effective by virtue of thedifferent diameter portions of the inner wall surface of the cylinderand the corresponding different effective diameters of the sealing meansto provide a fluid bias urging the piston toward the stop means whichreleasably retains the piston at the first end of the cylinder in itsnormal position, the pressurized fluid from said air return space beingexhausted to the atmosphere when the piston is returned to its normalposition.

(page 3 of 3 pages) Signed and sealed this 11th day of July 1972,.

(SEAL) Attes t:

EDWARD M .FLETCHER,JP.. ROBERT GOTTSGHALK Attesting Officer Commissionerof Patents

1. In a fastener driving tool of the type using an impulse ofpressurized fluid for returning a piston from a displaced position to anormal position in which the piston is to be retained, said pistonhaving a single effective diameter during its movement between saiddisplaced and normal positions, said single effective diameter beinglocated at an upper portion of said piston, a cylinder in which thepiston is slidably mounted, said cylinder having a first end portionoccupied by the piston in its normal position and a second end portionoccupied by the piston in its displaced position, said cylinder havingat its type using an impulse of a pressurized fluid for returning apiston from a displaced position to a normal position in which thepiston is to be releasably retained, said piston having a singleeffective diameter during its movement between said displaced and normalpositions, said single effective diameter being located at an upperportion of said piston, a cylinder in which the piston is slidablymounted, said cylinder having a first end portion occupied by the pistonin its normal position and a second end portion occupied by the pistonin its displaced position, said cylinder having at its first end portionand spaced from an intermediate portion of the cylinder through whichthe piston moves in moving to the displaced position an inner wallsurface with greater and lesser diameter portions, the remaining innersurface of the cylinder in said intermediate portion being of asubstantially uniform diameter generally corresponding to said singlediameter, said cylinder having port means at said second end portion, apair of spaced sealing means on the piston slidably engaging the innerwall surface of the cylinder and defining a fluidreceiving spacetherebetween, at least one of the sealing means being expansible andcompressible, an air return space communicating with the interior of thecylinder at the second end portion through the port means, first stopmeans for arresting movement of the piston in said displaced positionwith the piston adjacent the port means, return means for providingpressurized fluid to said air return space which passes through saidport means to provide said impulse of pressurized fluid to return thepiston to its first end portion and spaced from an intermediate portionof the cylinder through which the piston moves in moving to thedisplaced position an inner wall surface with greater and lesserdiameter portions, the remaining inner surface of the cylinder in saidintermediate portion being of a substantially uniform diameter generallycorresponding to said single diameter, a pair of spaced sealing means onthe piston slidably engaging the inner wall surface of the cylinder anddefining a fluid receiving space therebetween, at least one of thesealing means being expansible and compressible, piston return means forsupplying an impulse of pressurized fluid for returning the piston fromthe displaced position to the normal position, stop means on the toolfor arresting return movement of the piston in the normal position withthe pair of spaced sealing means engaging the different diameterportions of the inner wall surface of the cylinder, and air-supplyingmeans for supplying pressurized fluid to said space between the pair ofsealing means which is effective by virtue of the different diameterportions of the inner wall surface of the cylinder and the correspondingdifferent effective diameters of the sealing means to provide a fluidbias urging the piston toward the stop means which releasably retainsthe piston at the first end of the cylinder in its normal position. 2.The fastener driving tool set forth in claim 1 in which the cylinder hasa step formed in the inner wall surface to provide the greater andlesser diameter portions.
 3. The fastener driving tool set forth inclaim 1 in which the cylinder has a tapered inner wall surface providingthe greater and lesser diameter portions.
 4. The fastener driving toolset forth in claim 1 in which the air-supplying means includes valvemeans carried on the piston.
 5. The fastener driving tool set forth inclaim 4 in which the valve means includes the sealing means disposedadjacent the greater diameter portion of the inner wall surface of thecylinder when the piston is in its normal position.
 6. The fastenerdriving tool set forth in claim 1 in which the air-supplying meansincludes a fluid pressure supplying passage passing through the cylinderand opening into the cylinder at said first end portion.
 7. The fastenerdriving tool set forth in claim 1 in which the air-supplying meansincludes a unidirectional valve communicating with said space at one endand the interior of the cylinder above the piston at the other end. 8.In a fastener driving tool of the normal position, second stop means onthe tool for arresting return movement of the piston in the normalposition with the pair of spaced sealing means engaging the differentdiameter portions of the inner wall surface of the cylinder, andair-supplying means for supplying pressurized fluid to said spacebetween the pair of sealing means which is effective by virtue of thedifferent diameter portions of the inner wall surface of the cylinderand the corresponding different effective diameters of the sealing meansto provide a fluid bias urging the piston toward the stop means whichreleasably retains the piston at the first end of the cylinder in itsnormal position, the pressurized fluid from said air return space beingexhausted to the atmosphere when the piston is returned to its normalposition.
 9. The fastener driving tool set forth in claim 8 in which thereturn means includes means controlled by the piston for supplying airto the air return space when the piston is in its displaced position.10. The fastener driving tool set forth in claim 8 in which the returnmeans includes a valve carried on the piston for supplying pressurizedfluid to the air return space.
 11. The fastener driving tool set forthin claim 8 in which a valve carried on the piston forms a part of boththe return means and the air-supplying means for supplying pressurizedfluid to both the air return space and the fluid receiving space.
 12. Afastener driving tool as set forth in claim 8 in which the air-supplyingmeans includes a passage through the first end portion of the cylindercommunicating with the fluid-receiving space.
 13. A fastener drivingtool as set forth in claim 8 in which a fluid pressure reservoircontinually supplied with pressurized fluid is disposed adjacent thefirst end portion of the cylinder, and the fluid-supplying meansincludes a passage through the first end portion of the cylinder betweenthe reservoir and the fluid receiving space.
 14. In a fastener drivingtool of the type in which a piston is reciprocated between a normalposition in which the piston is to be releasably retained and adisplaced position, said piston having a single effective diameterduring its movement between said normal and displaced positions, acylinder in which the piston is slidably mounted, said cylinder having afirst end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having only at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position a part of its inner wall surface withgreater and lesser diameter portions, stop means on the tool forarresting return movement of the piston in the normal position, a pairof spaced sealing means sealing the piston-cylinder interface when thepiston is in said normal position and defining a fluid-receiving spacetherebetween, the pair of sealing means being so spaced as to provideseals at the different diameter portions of the inner wall surface ofthe cylinder, at least one of the sealing means being carried on thepiston and being expansible to different diameters to slidably engagethe inner wall of the cylinder during the reciprocating movement of thepiston, and air-supplying means for supplying pressurized fluid to thespace between the pair of sealing means which is effective by virtue ofthe different effective diameters of the piston to provide a fluid biasurging the piston toward the stop means which releasably retains thepiston at the first end portion of the cylinder in its normal position.15. The fastener driving tool set forth in claim 14 in which the othersealing means is carried on the cylinder at its first end portion toengage the piston only when the piston is in its normal position. 16.The fastener driving tool set forth in claim 14 in which the cylinderhas a substantially uniform diameter equal to said lesser diameter, andthe greater diameter portion at said first end portion of the cylinderis formed by an undercut portion spaced slightly below the end of thecylinder.
 17. The fastener driving tool set forth in claim 14 in whichthe air-supplying means includes a passage extending through the wall ofthe cylinder and supplied with pressurized fluid.
 18. In a fastenerdriving tool of the type in which a piston is reciprocated between anormal position in which the piston is to be releasably retained and adisplaced position, said piston having a single effective diameterduring its movement between said normal and displaced positions, acylinder in which the piston is slidably mounted, said cylinder having afirst end portion occupied by the piston in its normal position and asecond end portion occupied by the piston in its displaced position,said cylinder having at its first end portion and spaced from anintermediate portion of the cylinder through which the piston moves inmoving to the displaced position a part of its inner wall surface withgreater and lesser diameter portions, stop means on the tool forarresting return movement of the piston in the normal position, a pairof spaced sealing means sealing the piston-cylinder interface when thepiston is in said normal position and defining a fluid-receiving spacetherebetween, the pair of sealing means being so spaced as to provideseals at the different diameter portions of the inner wall surface ofthe cylinder, at least one of the sealing means being carried on thepiston and being movable between a first diameter only when the pistonis in said normal position and a second different and constant diameterto slidably engage the inner wall of the cylinder during thereciprocating movement of the piston through said intermediate portionof the cylinder, first means for supplying pressurized return fluidbelow the piston to move the pistoN from its displaced position to itsnormal position, and second means for supplying a part of saidpressurized return fluid to the space between the pair of sealing meanswhich is effective by virtue of the different effective diameters of thepiston to provide a fluid bias urging the piston toward the stop meanswhich releasably retains the piston at the first end portion of thecylinder in its normal position.
 19. The fastener driving tool set forthin claim 18 in which both of the sealing means are carried on thepiston, and the sealing means that engages the lesser diameter portionof the cylinder provides a check valve in said second means forsupplying a part of the pressurized return fluid to said fluid-receivingspace.
 20. The fastener driving tool set forth in claim 19 in which thesealing means engaging the greater diameter portion of the cylinderprovides a check valve forming a part of said first means for supplyingpressurized return fluid below the piston.